Plastic container closures and, more particularly, plastic closures for carbonated beverage bottles having threaded necks are well known, having previously been disclosed, for example, in U.S. Pat. Nos. 4,310,101; 4,326,639; 4,394,918; 4,461,391; and 4,476,987. Such closures typically employ sealing discs and/or molded flanges which contact the bottle lip to reduce the loss of carbonation through the space between the closure and the bottle finish. Used alone, integrally molded plastic flanges have not provided the desired sealing characteristics. Although sealing discs have proved to be quite effective for reducing loss of carbonation, they are usually separately manufactured and then inserted into a molded bottle cap, thereby increasing both the time and expense required to produce a satisfactory closure. A unitarily molded plastic bottle cap having improved sealing characteristics is disclosed in U.S. Pat. No. 4,744,478.
Notwithstanding the advantages achieved with the moldable plastic closures having an integrally molded foam layer, manufacturers may require closures that are adapted to further retard the migration of oxygen or carbon dioxide through the closure without appreciably increasing thickness or weight of the closure. In other instances, manufacturers may desire lighter or thinner closures having an equivalent or better capability to retard oxygen or carbon dioxide migration.
The processes for making many plastic closures such as soft drink bottle caps, other bottle caps, jar lids and the like usually include injection molding of the basic lid, followed by installation of some sort of gasket material to provide a tight seal between the bottle finish and the cap or lid. When utilized in this manner, permeable gasket materials frequently do not adequately retard the migration of certain gasses, either resulting in loss of carbon dioxide (from soft drinks) or the infusion of oxygen (into food products and other beverages). In either instance, the quality of the product within the container may be significantly degraded or deteriorated.
Plastic closures are therefore needed that comprise at least one substantially unfoamed polymer layer integrally molded to at least one foamed layer of the same polymer, and further comprise a coating adapted to further retard the migration of oxygen and carbon dioxide through the closure. Alternatively, plastic closures without foamed layers are needed that employ one or more barrier layers to retard the migration of gasses such as oxygen and carbon dioxide through the closure.